1. Field of the Invention
The present invention relates to an exposure device used in the process of producing semiconductors, liquid crystal substrates, color films and the like, particularly relates to an exposure device provided with a light source for emitting light in the ultraviolet region, for example, wherein laser light is used as a means for supplying energy to the light source.
2. Description of Related Art
Progress has recently been made for reducing treatment time and subjecting an object to be treated having a large area to one-shot exposure in the process for producing semiconductors, liquid crystal substrates, color films and the like using an ultraviolet light source, which has a large input voltage. Accordingly, there is a need for the emission of light having a higher intensity of a high-pressure discharge lamp, which is a UV light source. However, the problem associated with simply increasing an input voltage applied to a high-pressure discharge lamp is that the load applied to the electrodes disposed within the discharge vessel increases, leading to the production of vaporized material from the electrodes. As a result, the high-pressure discharge lamp may be blackened and its lifetime reduced.
A wide variety of proposals have been made for solving the above-mentioned problems. As an example, JP-A-61-193385 discloses a method for emitting light by disposing an electrodeless discharge lamp inside an elliptical reflector and emitting laser light to a discharge vessel of the discharge lamp through a opening part provided on the side face of the elliptical reflector to excite a discharge gas sealed inside the discharge vessel. This technology enables to avoid the problem that the lifetime of the lamp is reduced, which is caused by the blackening of the discharge vessel caused by the evaporation of electrode material while the lamp is on, as no electrode is used inside the discharge lamp. Thus, the advantage of this technology is that a discharge lamp having a long lifetime can be provided.
FIG. 6 shows the constitution of the electrodeless discharge lamp disclosed in JP-A-61-193385 at the time of emitting laser light as one example of semiconductor exposure devices using an electrodeless discharge lamp based on laser excitation. The semiconductor exposure device 101 is composed of a laser oscillator 102, an optical component 103 for adjusting laser light emitted from the laser oscillator 102 to a desired diameter, an optical component 104, a condenser lens 105 for condensing the laser light, an electrodeless discharge lamp 106 for emitting the laser light condensed by the condenser lens 105, an elliptical reflector 107 for reflecting ultraviolet light emitted from the electrodeless discharge lamp 106, and an optical system 108 for emitting the ultraviolet light reflected by the elliptical reflector 107 to a semiconductor wafer 121, an article to be treated. Moreover, the elliptical reflector 107 is provided with a laser beam inlet 110a for the incident laser light and a laser beam outlet 110b for exiting laser light, which is not absorbed by the elliptical reflector 107 and passes therethrough, to the outside of the elliptical reflector 107. The laser light exiting from the laser beam outlet 110b is absorbed by a light absorbing plate 109 to be converted into heat, for example, so that the laser light cannot be brought back to the laser oscillator 102.
However, the arrangement disclosed in JP-A-61-193385, as shown in FIG. 6, has the following problem. In order to supply energy to the electrodeless discharge lamp 106, the side faces of the elliptical reflector 107 are provided with the laser beam inlet 110a and the laser beam outlet 110b, and laser light is emitted to the electrodeless discharge lamp through the openings 110a, 110b. Hence, the problem is that the provision of the openings 110a, 110b on the side faces of the elliptical reflector 107 leads to a decline in the original function of the elliptical reflector 107, i.e., condensing ultraviolet light generated from the electrodeless discharge lamp. In other words, the generated ultraviolet light cannot effectively be utilized.
Furthermore, if the openings 110a, 110b provided on the elliptical reflector 107 are made small, the angle of incidence of laser light on the electrodeless discharge lamp 106 becomes small. In the event of emitting high energy, the energy density of laser light passing through the discharge vessel becomes too high, which may lead to various problems including a hole being generated in the discharge vessel of the lamp. If the openings 110a, 110b are made large for the incoming laser light in order to reduce the energy density of the laser light, the problem is that ultraviolet light emitted from the electrodeless discharge lamp 106 cannot effectively be used, as described above.